1. Field of the Invention
The present invention relates in general to compressors for use in an automotive air conditioning system or the like, and more particularly to compressors of a variable displacement swash plate type.
2. Description of the Prior Art
Japanese Patent First Provisional Publications 8-61231 and 6-101640 show compressors of a variable displacement swash plate type, which comprise a drive shaft, a sleeve axially movably disposed on the drive shaft, a journal swingably disposed on the sleeve, a swash plate held by the journal to rotate together with the drive shaft while assuming an inclined position relative to the drive shaft, a plurality of cylinders arranged at evenly spaced intervals about an axis of the drive shaft, and a plurality of pistons respectively received in the cylinders and reciprocatively driven by the swash plate. For achieving the swinging movement of the journal on the sleeve, the sleeve has a convex outer surface with which a concave inner surface of the journal is slidably engaged. That is, a so-called "convex-concave surface sliding structure" is provided between the sleeve and the journal. With this structure, a satisfied inclination of the swash plate relative to the drive shaft is achieved with a compact unit including the journal and the sleeve.
However, as is known, due to difficulty with which the convex and concave surfaces are machined, manufacturing of such convex-concave surface sliding structure requires a skilled and thus costly processing technique. In particular, the processing of the concave surface is quite difficult.
Furthermore, it tends to occur that the mutually engaging surfaces encounter a lack of lubrication oil. That is, when the compressor is used in the air conditioning system, the lubrication oil is dispersed in a refrigerant compressed by the compressor. However, due to the nature of the convex-concave surface sliding structure, the mutually engaging surfaces tend to fail to receive a sufficient amount of lubrication oil from the refrigerant.